Field of the Invention
The present invention relates to a process for manufacturing tyres for vehicle wheels.
The invention further relates to a process and an apparatus for reinforcing with a loop an annular anchoring structure of a tyre for vehicle wheels, said process and said apparatus being usable in carrying out the above process for manufacturing the tyre.
Description of the Related Art
A tyre for vehicle wheel generally comprises a carcass structure comprising at least one carcass ply comprised of reinforcing cords embedded in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures arranged in the zones usually identified with the name of “beads” and normally consisting each of a substantially circumferential annular insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular inserts are commonly identified as “bead cores” and have the task of keeping the tyre firmly fixed to the anchoring seat specifically provided in the rim of the wheel, thus preventing, in operation, the radially inner end edge of the tyre coming out from such a seat.
At the beads specific reinforcing structures (known, in the field of tyres, by the term: loops) may be provided, these reinforcing structures having the function of improving the torque transmission to the tyre. In fact, the bead region is particularly active in the torque transmission from the rim to the tyre during acceleration and braking, and therefore the provision of proper reinforcing structures in such zone ensures that the torque transmission takes place with the maximum possible reactivity.
In a radially outer position with respect to the carcass ply, a belt structure comprising one or more belt layers is associated, said belt layers being arranged radially one on top of the other and having textile or metal reinforcing cords with crossed orientation and/or an orientation substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure a layer of elastomeric material, known as “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made of elastomeric material as well other structural elements making up the tyre.
Between the tread band and the belt structure a so-called “under-layer” of elastomeric material can be arranged, said under-layer having properties suitable for ensuring a steady union of the tread band itself.
On the side surfaces of the carcass structure respective sidewalls of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
The traditional processes for manufacturing tyres for vehicle wheels essentially provide for the components of the tyre listed above to be first made separately from one another, to be then assembled in a subsequent building step of the tyre.
However, the current tendency is that of using manufacturing processes that allow the manufacturing and storage of semi-finished parts to be minimised or possibly eliminated. In such processes, each component of the tyre is directly formed on a forming support, for example as illustrated in EP 0 928 680 in the name of the same Applicant.
More specifically, attention has now turned towards process solutions that allow the individual components of the tyre to be made by directly building them, according to a predetermined sequence, onto the tyre being built on a forming support, typically toroidal or cylindrical.
For example, WO 2009/040594 in the name of the same Applicant, shows a process wherein the different building steps of the carcass structure are carried out at least in part simultaneously with the steps of making the crown structure at respective separate work stations, wherefrom the respective products must come out in a synchronised manner so as to proceed with the subsequent step of assembling the crown structure on the carcass structure and then, with the subsequent steps of the process for manufacturing the tyre.
Throughout the present description and in the following claims, the term “loop” is used to indicate an annular element comprising one or more thread-like reinforcing elements substantially parallel to one another, such as textile or metal cords, optionally embedded in, or coated with, a layer of elastomeric material, such annular element being obtained by cutting to size a band-like element and reciprocally joining a head portion and a tail portion of such band-like element.
The term: “elastomeric material” on the other hand is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition further comprises additives such as, for example, a cross-linking agent and/or a plasticizer. Thanks to the provision of the cross-linking agent, such material may be cross linked by heating, so as to make the end product.
Throughout the present description and in following claims, the terms “radial” and “axial” and the expressions “radially inner/outer” and “axially inner/outer” are used by making reference to the radial direction and to the axial (or longitudinal) direction of a tyre (or of a drum used for building the tyre or one or more components of the tyre). The terms “circumferential” and “circumferentially” instead, are used by making reference to the annular extension of the tyre/drum.
U.S. Pat. No. 5,632,836 shows, in FIG. 1, a loop 6 wound about an annular anchoring structure 5, the latter comprising a plurality of bead cores 3 and a filling insert 4.
EP 0 647 522 shows, in FIG. 7, a loop 32 wound about an annular anchoring structure, the latter comprising a plurality of bead cores 30 and a filling insert 31. Loop 32 is first deposited on the annular outer surface of a service drum 6. The annular anchoring structure is then positioned on the loop 32. Loop 32 is then turned up about the annular anchoring structure by the effect of the thrust action exerted by lobes 11, 18 of the air tube 7 on the portions of loop 32 which axially extend from opposite sides with respect to the annular anchoring structure. Lobes 11, 18 are obtained by inflating an air tube 7 against a pair of annular bells 19, 20.